POS0888 NORMAL PERCENTILE REFERENCE CURVES FOR SKIN ULTRASOUND THICKNESS AND STIFFNESS AT RODNAN SITES
Authors: T. Santiago, E. Santos, M. Luis, C. Gaspar, J. Lima, F. Caramelo, J. A. P. Da Silva
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Skin involvement is a hallmark of systemic sclerosis and an important marker of disease activity, severity and prognosis.<sup>[1]</sup> The modified Rodnan skin score (mRSS), the current gold standard for the evaluation of the skin in SSc, both in clinical trials and in practice, has several limitations.<sup>[2]</sup> This highlights the need for more sensitive and objective measures of skin involvement, not only support the evaluation and development of new treatments, but also to facilitate the earlier diagnosis of SSc. Normal reference curves for skin ultrasound parameters, considering relevant influential factors seem of pivotal importance to fully exploit the potential of these new techniques as reliable tools for diagnostic and follow-up purposes. <h3>Objectives</h3> Our primary objective was to establish preliminary normal reference curves for ultrasound dermal thickness and skin stiffness, in the 17 Rodnan skin sites, considering the effect of gender and age on these measures. As an exploratory objective, we investigated the effect of body mass index and the menopause on skin ultrasound measures. <h3>Methods</h3> A cross-sectional study was conducted involving 140 healthy volunteers, aged 20-79 years. Recruitment was stratified for age (10-year categories) and gender to guarantee a balanced distribution of these factors in the sample. participants were excluded if they had any of the following conditions: (1) diagnosis of any skin or connective tissue or rheumatic inflamma- tory disease, (2) history of insulin treated diabetes, (3) history of anticancer chemo/radiotherapy treat- ments, (4) exposure to organic solvents, (5) past glucocorticoid treatment for more than 4 months or (6) recent (&lt;4 weeks) treatment with glucocorticoids, regardless of dose, clinical indication and timing. Ultrasound dermal thickness and skin stiffness were assessed by high-frequency ultrasound (18MHz) and shear-wave elastography (9MHz), respectively, at the 17 Rodnan skin sites. All ultrasound measures were performed in the morning (between 9:00 and 13:00 hours) in the same room and at stable temperature. Outcomes were evaluated through a mixed linear model, univariate, and multivariate regressions. Normal reference curves were derived for both ultrasound measures in each Rodnan skin site, for females and males (Example in Figure 1). An online calculator of the percentiles of skin ultrasound measures was also developed. A radar chart showing these values and the percentile for each site is automatically drawn, allowing the clinician to export the results obtained. <h3>Results</h3> A total of 140 caucasian participants, i.e., 80 females, mean (SD) age of 47.2 (16.0) years; and, 60 males, 49.5 (17.3) years were included. Ultrasound dermal thickness and stiffness measures were higher in males than females, in all Rodnan skin sites (except in chest for ultrasound-dermal thickness). Age had also a significant impact in both ultrasound measures, but only in some skin sites. Gender and age percentile curves (97.5<sup>th</sup>, 95<sup>th</sup>, 75<sup>th</sup>, 50<sup>th</sup>, 25<sup>th</sup>, 5<sup>th</sup>, 2.5<sup>th</sup>) were plotted for each of the measures in each skin site. <h3>Conclusion</h3> Gender and age are strongly associated with skin ultrasound parameters, imposing the need for gender- and age-specific reference values. Normal reference percentile curves for skin ultrasound measures are promising tools to support earlier diagnosis and refine sensitivity to time- or drug-induced changes. These reference percentile curves are provided as a basis for future cooperative work to strengthen its evidence-basis, representativeness and refinement regarding potentially influential factors. <h3>References</h3> [1]doi:10.1038/nrdp.2015.2; [2]doi:10.5301/jsrd.5000231; [3]doi:10.1002/acr.2359 <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> None Declared.